In guaranteed tailcall mode, don't decline the tailcall optimization

for blocks ending in "unreachable".

llvm-svn: 95565

1 files changed, 10 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index cf342c793b9..93ae043dbc1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4205,13 +4205,16 @@ isInTailCallPosition(CallSite CS, Attributes CalleeRetAttr,
   const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
   const Function *F = ExitBB->getParent();
 
-  // The block must end in a return statement.
-  // FIXME: Disallow tailcall if the block ends in an unreachable for now.
-  // The way tailcall optimization is currently implemented means it will
-  // add an epilogue followed by a jump. That is not profitable. Also, if
-  // the callee is a special function (e.g. longjmp on x86), it can end up
-  // causing miscompilation that has not been fully understood.
-  if (!Ret) return false;
+  // The block must end in a return statement or unreachable.
+  //
+  // FIXME: Decline tailcall if it's not guaranteed and if the block ends in
+  // an unreachable, for now. The way tailcall optimization is currently
+  // implemented means it will add an epilogue followed by a jump. That is
+  // not profitable. Also, if the callee is a special function (e.g.
+  // longjmp on x86), it can end up causing miscompilation that has not
+  // been fully understood.
+  if (!Ret &&
+      (!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
 
   // If I will have a chain, make sure no other instruction that will have a
   // chain interposes between I and the return.